This invention relates generally to gas turbine engines, and, more specifically, to a gas turbine engine with an intermediate pressure fan stage having a tip fan located on a blade driven by a pressurized airflow.
In a turbofan aircraft gas turbine engine, air is pressurized in a fan module, an optional booster module and a compression module during operation. A portion of the air passing through the fan module is passed into a by-pass stream and used for generating a portion of the thrust needed for propelling an aircraft in flight. The air channeled through the optional booster module and compression module is mixed with fuel in a combustor and ignited, generating hot combustion gases which flow through turbine stages that extract energy therefrom for powering the fan, booster and compressor rotors. The fan, booster and compressor modules have a series of rotor stages and stator stages. The fan and booster rotors are typically driven by a low-pressure turbine (LPT) and the compressor rotor is driven by a high-pressure turbine (HPT). The fan and booster rotors are aerodynamically coupled to the compressor rotor although the fan rotor and compressor rotor normally operate at different mechanical speeds.
It is often desirable to use an engine core comprising the compressor, combustor, high-pressure turbine (HPT) and low-pressure turbine (LPT) from a high bypass commercial engine or a medium bypass engine with a moderate fan pressure ratio as a building block for lower bypass ratio engines with higher fan pressure ratios. The boost pressure and temperature into the high-pressure compressor (HPC) is usually significantly higher in the low-bypass derivative engine than in the original high-bypass engine. This typically requires that the maximum operating airflow in the core be limited below its full design corrected airflow capacity due to mechanical limitations of the maximum physical core speed and/or the maximum compressor discharge temperature capability of the core. It is desirable to find a way to operate the original engine core airflow at its full potential while significantly increasing the fan pressure ratio to the bypass stream to maximize the thrust potential of the derivative engine.
Accordingly, it would be desirable to have a fan system that makes it possible to operate the original engine core near its full airflow capability while significantly increasing the fan pressure ratio to the bypass stream to maximize the thrust potential of the derivative engine.